In recent years, there has been an increase in demand for corrosion resistant steel and processes of treating steel to impart corrosion resistance. High speed electroplating methods typically use high current densities. This type of electroplating method requires a rapid system for supplying the consumed electrolyte. Generally, this method uses an insoluble electrode and feeds the electrolyte into the bath in a soluble form.
An acid, such as sulfuric acid, is often used in electroplating zinc baths. The zinc is usually supplied as zinc oxide that is dissolved or dispersed in water and then dissolved in the sulfuric acid. Metallic zinc can be added to the acid bath which will dissolve in the sulfuric acid. Zinc in metal form is generally less preferred since the metallic zinc dissolves slowly in sulfuric acid and is not suitable for high production plating devices.
Conventional electroplating plants usually include a mixing tank, separate from the treating bath, for dissolving the metal source in the plating bath. The mixing tanks typically include an agitator and a steam connection for dissolving the metal source. The metal source is usually added in the form of a metal salt. The metal salts are dissolved in hot water and then transferred to the tank for the treating bath. Some metal compounds, such as zinc oxide, cannot be added directly to the acid bath and must first be dissolved in hot water.
The metal salts and metal compounds are often toxic and product large quantities of dust when added to the mixing tank. The metal salts are usually supplied in containers such as barrels or bags which expose the workers to large amounts of toxic dust, thereby increasing the health risks to the workers.
Modern electroplating plants using insoluble anodes require continuous resupplying of the metals being deposited on the substrate. The metals must be supplied to the plating bath either by dissolving the metal directly or by the addition of galvanic salts. In a similar manner, conducting salts also must be added continuously to the electrolyte bath to increase the conductivity of the electrolyte bath and reduce the electrical power consumption. The conducting salts are continuously depleted during the plating process with the primary plating metal and must be replenished.
High output plants typically use a silo and an automatic weighing device to supply the salts to the bath. The plants also include a dosing device to feed the salts to the dissolving tank. The tanks require expensive dust recovery devices to prevent the escape of dust particles to the atmosphere. The handling of the toxic dust particles complicates the operations and operating costs.
The prior large scale plants and the feeding and mixing arrangements form lumps in electrolyte bath when the salts are added. The agitating devices in the mixing tanks are not always able to prevent the formation of lumps in the bath.
Accordingly, there is a continuing need in the industry for improved systems for electrochemical treatment plants.